Duplex control circuit



P 1947. M.YG. NICHQLSON, JR 2,428,126

DUPLEX CONTROL C IRCUIT Filed July 21, 1944 module $07 v I N VEN TOR. 77/011307? 6f 7718305022. J:

Patented Sept. 30, 1947 DUPLEX CONTROL CIRCUIT Madison G. Nicholson, In, Kenmore, N. Y., as-

signor to Colonial Radio Corporation, Buffalo,

Application July 21, 1944, Serial No- 546,008

7 Claims. 1

This invention relates to duplex control circuits, and more particularly to such circuits as employed to control a transmitter which may operate with either of two distinctive characteristics; that is to say, he transmitter may be controlled by a pair of modulators A and B, which, for the purposes of this application, may be assumed to control the transmitter to give distinctive characteristics peculiar to the particular-modulator in control; for instance, modulator A may cause the transmitter to transmit a predetermined number of pulses of predetermined length and with a predetermined time interval between them. whereas modulator B may cause the transmitter to transmit at the same frequency but with a different predetermined number of pulses or with a different predetermined time interval between them.

It is desired to provide a control circuit which will permit operation of either modulator at will, as may be desired, but it is also important to prevent blocking of the modulators or improper or faulty operation which might occur provided the control keys for both modulators were operated at the same time. Since only one modulator can be permitted to occur at a time on the transmitter, it is necessary to provide arrangements for locking one out when the other is in.

At the same time, to prevent one modulator being rendered inoperative, it is desirable to provide control circuits whereby these modulators may be alternately operable in turn for a period or time which is sufiicient to permit them to send out the desired signal.

For example, in the operation of my control circuit, supposing, that two keys controlling the two modulators are closed simultaneously, under such conditions that one modulator will cause the transmitter to send out thesignal characteristic of the operating modulator, and after this action is completed, control is transferred to the other modulator, which causes the transmitter to send out a signal modulated with the characteristic of the other modulator, and the entire process of operation may be completed in an extremely short period of time; for example, of the order of /100 of a second.

Thus, while the two modulators act successively an never simultaneously in point of time, yet their operations follow each other so quickly that for all practical purposes they may be regarded as simultaneous, and this in effect provides for duplex operation of one transmitter.

It is an object of this invention to provide a duplex control circuit which will prevent one modulator from controlling the transmitter while the other is in control.

It is a further object of this invention to provide such a circuit in which the operation of the second modulator, although temporarily prevented from occurring while the first modulator is in control of the transmitter, will, nevertheless, operate within an extremely short interval of time after the control key is operated.

It is still a further object of my invention to provide a control circuit for applying two modulators to a transmitter alternately for very short periods of time whereby in effect duplex operation is provided.

Still other objects and advantages of my invention will be apparent from the specification.

The features of noveltywhioh I believe to be characteristic of my invention are set forth with particularity in. the appended claims. My invention itself, however; both as to its fundamental pr-incii lsa'nd as til its particular embodiments, will best" be understood by reference to the specification and accompanying drawing, in which I The single fi ure is a cim'uit diagram of a anplex control s stem in accordance with my invention.

Referring ir'ior partifilarly to the drawing, Il may represent the control key or switch to control modulator A. Modulator A is not shown in detail since it orms per se no part of this invention, but it will be understood that it is put into operation by closure of relay contacts l3c of relay l3.

Relay I3 is controlled by the operationof tube l2, which may be a gas-filled tube of the thyratron type, having cathode I20, control grid I29, screen grid IE9, and anode 12a. Cathode I20 may be connected to ground through resistance l6 and through resistance I! to the +13 source of supply. Control grid |2g may be connected directly to ground, and screen grid lisg through a difierentiating'network to a multivibrator' which will be described hereafter.

Cathode I26 may, likewise, be connected through resistance is and switch H to ground.

to ground through resistance 26 corresponding to resistance [6 and through resistance 21 corresponding to resistance I! to the +13 source of supply and through resistance 25 corresponding to resistance I5 and through switch'Zl to ground. Control grid 229 may be connected directly to ground and screen grid 2289 through a difierentiating network to multivibrator 30. Anode 22a may be connected through the solenoid of relay 23 shunted by condenser 24 to the +3 supply.

Multivibrator 30 may comprise a pair of tubes 3| and 32, tube 3| having cathode 3|c, control grid 3|g, and anode 3|a, and tube 32 having cathode 32c, grid 32g, and anode 32a. Each of the cathodes 3|c and 320 may be connected directly to ground, and each of the anodes 3|a and 32a may be connected through resistances 31 and 38 to the +3 supply.

Each of the grids 3|g and 32g may be connected to ground through resistances 33 and 35 respectively, and the grid of each tube is connected to the anode of the other through condensers 34 and 36. Anode 3|a may be connected to grid |2sg through condenser 4| and grid |2sg connected to ground through resistance 40. Similarly grid 22sg may be connected to anode 32a through condenser 43 and connected through resistance 42 to ground. These resistance-condenser networks form a difierentiation network serving to produce pulses from the output of the multivibrator which operates to produce a square wave or substantially square wave of 25 pulses per second.

The voltage drop through resistances l6 and 26 serves to maintain a cathode grid potential difference n tubes i2 and 22 so that they cannot be ionized when the keys II and 2| are open, and it will be noted that the voltage drop through these resistances is derivedfrom the +13 source through bleeder resistances l1 and 21.

When, however, keys H or 2| are closed, resistances l6 and 26 are shunted by the path formed by resistance l and key N on the one hand or resistance 25 and key 2| on the other, the value of these resistances being relatively low as compared with resistances l6 and 26 whereby, when either key is closed, the potential of the respective cathodes, which was formerly above ground, now approaches ground. At this point either of the thyratrons may be fired by a pulse applied to the screen grids |2sg and 228g from the multivibrator through condensers 4| and 43 respectively.

It will be understood that the potential of the anodes 3|a. and 32a with the multivibrator in operation is 180 out of phase, so that when a positive pulse is applied to the grid |2sg through condenser 4|, 9. negative pulse is applied to the grid 22sg through condenser 43. In other words, these grids may be regarded as opposite ends of a see-saw driven by the multivibrator, and they cannot both go positive at the same time.

The operating voltages are so chosen that when key or 2| is closed, the next positive pulse will fire the tube. For instance, if key N is held closed, tube |2 will not fire until a positive pulse is received, but as soon as one is received while the key is closed, the tube |2 will fire.

At this point it may be noted that condensers i4 and 24 are relatively large in capacity, and are so related to the windings of relays l3 and 23 that the charge accumulated on the condenser when the tube fires is such as to hold the relay closed for an appreciable period of time; that is, during the interval between successive positive pulses.

Consequently, if key or 2| be closed, the tube l2 or 22 will fire on the next positive pulse applied to its grid, and this current will charge the relay shunting condenser and close the relay within a few milliseconds after the pulse is applied to the grid.

The drop in plate voltage resulting from the current across the tube will cause deionization of the tube but the relay continues in closed position, being held closed by the flow of current from its respective condenser, and this operation will continue so long as one key is held closed.

For instance, if key N is closed, tube |2 will fire on the next positive pulse and relay 3 will operate and close contacts |3c. At the next positive pulse the action repeats itself, the tube firing, charging condenser I4, and then deionizing, so that as long as key is held closed, relay contacts |3c will remain closed.

The same is true of key 2|. As long as it is held closed, contacts 230 will be closed and remain closed through an entirely similar action; but while these circuits are closed at contacts |3c or at 230, the modulator does not continue to control the transmitter, the type of modulation here employed being such that the modulation is completed in not more than 20 milliseconds.

This is analogous to a magnet having a bell clapper arranged to strike a bell but having no interrupter in the circuit, so that it strikes once only when the circuit is closed, and will not strike again no matter how long the circuit is left closed. It will be seen, therefore, that if switches H and 2| are closed simultaneously, it is a matter of chance which modulator will operate first, the first being the one which first receives the positive pulse on the grid of its control tube.

Assume now that switches II and 2| are both closed at the same identical instant. At this point we may assume that |2sg is about to receive a, positive pulse. Therefora grid 22sg is about to receive a negative pulse. When these pulses occur, tube |2 will ionize and contacts |3c will close and modulator A will impress its characteristic modulation on the transmitter, this occurring and being completed within 20 milliseconds.

Assuming that switches H and 2| are still held closed, as soon as grid 22sg receives a positive pulse, tube 22 will fire and contacts 230 will close and modulator B will then impress upon the transmitter its characteristic modulation which will be completed within 20 milliseconds thereafter.

Thereupon no further modulations will be impressed by either modulator because as long as keys H and 2| are held closed relays |3c and 230 will remain closed and no further modulations are impressed on the transmitter because, as stated, the nature of the modulations is such that they are impressed only for the first few milliseconds after closure of the respective relay contacts.

From this it will be understood that although keys II and 2| may be closed substantially simultaneously, first one modulator and then the other will operate and each will impress its characteristic modulation on the transmitter successively, and the whole operation takes place so rapidly that both modulations are made and completed in a time so short that they appear to occur simultaneously.

While I have shown and described certain preferred embodiments of my invention, it will be understood that modifications and changes may be made without departing from the spirit and scope thereof, as will be clear to those skilled in the art.

In particular, while I have shown my invention as applied to control a pair of modulators, it should be understood that my control circuit may be used to control other working elements under conditions where it may be desired to operate two elements selectively, to prevent simultaneous operation, and to provide for operation of both in rapid succession.

Also, while I prefer to employ gaseous discharge tubes, I may use high vacuum discharge tubes (hard tubes), and resistances in place of the relays, using the voltage pulses from the resistances for controlling the modulators.

In this application I have particularly pointed out and distinctly claimed the part, improvement, or combination which I claim as my invention or discovery, and I have explained the principles thereof and the best mode in which I have contemplated applying those principles so as to distinguish my invention from other inventions.

I claim:

1. The combination with a transmitter, of a pair of keying modulators, each arranged to impress its characteristic modulation on the transmitter, a pair of switches for controlling said modulators respectively, means for causing sequential operation of said modulators at a rate slower than the message keying rate when said switches are closed simultaneously, said last mentioned means including a pair of gaseous discharge tubes, each having a cathode, an anode, and a control electrode, means for generating a train of equally spaced positive pulses, and means for repeatedly applying successive pulses to the control electrode and cathode of alternate tubes respectively.

2. The combination with a transmitter, of a pair of keying modulators, each arranged to impress its characteristic modulation on the transmitter, a pair of switches for controlling said modulators respectively, means for causing sequential operation of said modulators at a rate slower than the message keying rate when said switches are closed simultaneously, said last mentioned means including a pair of gaseous discharge tubes, each having a cathode, an anode, and a control electrode, means for generating equally spaced positive pulses, a pair of relays in the space current circuit of said discharge tubes respectively, means for applying alternate positive pulses between the cathode and control electrode of one of said tubes, and means for applying the remaining positive pulses between the cathode and control electrode of the other of said tubes.

3. The combination with a transmitter, of a pair of keying modulators, each arranged to impress its characteristic modulation on the transmitter, a pair of switches for controlling said modulators respectively, means for causing sequential operation of said modulators at a rate slower than the message keying rate when said switches are closed simultaneously, said last mentioned means including a pair of gaseous discharge tubes, each having a cathode, an anode, and a control electrode, means for generating equally spaced positive pulses, a pair of relays in the space current circuit of said discharge tubes respectively, means for applying alternate positive pulses between the cathode and control electrode of one of said tubes, means for applying the remaining positive pulse between the cathode and control electrode of the other of said tubes, and a pair of capacities shunting the energizing winding of said relays respectively and of sufficient value to maintain said relays closed for an appreciable time after termination of space current in said tubes.

4. The combination with a transmitter, 01 a pair of modulators, each arranged to impress its characteristic modulation on the transmitter, a pair of switches for controlling said modulators respectively, means for causing sequential operation of said modulators when said switches are closed simultaneously, said last mentioned means including a pair of gas discharge tubes, each having a control electrode, a generator of substantially square waves, and a pair of difierentiating networks connected to said electrodes respectively and to points of 180 phase opposition in said square wave generator.

5. The combination with a transmitter, of a pair of modulators, each arranged to impress its characteristic modulation on the transmitter, a pair of switches for controlling said modulators respectively, means for causing sequential operation of said modulators when said switches are closed simultaneously, said last mentioned means including a pair of gas discharge tubes,

each having a pair of control electrodes; a generator of substantially square waves, means for applying alternately positive pulses from said square Wave generator to one of said control electrodes in each tube, the other of said control electrodes being normally biased with respect to the cathode of its respective tube so as to prevent ionization thereof, said switches being arranged to alter the bias on said last mentioned control electrode in the respective tubes to a value such that the tube will ionize when a positive pulse is applied to the other control electrode of said tube.

6. In a control circuit, in combination, a pair of gaseous discharge tubes, each having a cathode, an anode, and a pair of control electrodes, a generator of substantially square waves, a pair of differentiation circuits arranged to supply alternately positive pulses from said generator to one of the control electrodes of each of said tubes, a biasing resistor connected between the cathode of each of said tubes and ground, and a switch for closing a circuit of lower resistance in parallel with each of said biasing resistors.

7. In a control circuit, in combination, a pair of gaseous discharge tubes, each having a cathode, an anode, and a, pair of control electrodes, a multivibrator, a pair of differentiation circuits connected to said multivibrator and arranged to supply alternately positive pulses to one of the control electrodes of each of said tubes, a biasing resistor connected between the cathode of each of said tubes and ground, and a switch for closing a circuit of lower resistance in parallel with each of said biasing resistors.

MADISON G. NICHOLSON, JR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,407,399 Carlson et al Sept. 10, 1946 2,380,982 Mitchell Aug. 7, 1945 2,350,888 Hall June 6, 1944 2,365,450 Bliss Dec. 19, 1944 1,309,745 Potts July 15, 1919 Certificate of Correction MADISON G. NICHOLSON, JR.

It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows: Column 1, line 26, for occur read operate; column 2, line 4, for operate read occur; column 6, line 15, after the word and period generator. insert the following claim 5. The combination with a transmitter, of a pair of modulators, each arranged to impress its characteristic modulation on the transmitter, a pa1r of switches for controlling said modulators respectlv ely, means for causing Patent N 0. 2,428,126. September 30, 1947.

each having a control electrode; a substantially s uare wave generator, and means for impressing alternately upon said control electrodes positive pulses derived from the output of said square wave generator. for the claims now appearing in the patent as 5, 6 and 7 read 6, 7, and 8 respectively; in the heading to the printed specification, line 7, for 7 Claims read ims; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Ofiice.

Signed and sealed this 2d day of December, A. D. 1947.

THOMAS F. MURPHY,

Assistant Uommz'asioner of Patents.

Certificate of Correction Patent N 0. 2,428,126. September 30, 1947. MADISON G. NICHOLSON, JR.

It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows: Column 1, line 26, for occur read operate; column 2, line 4, for operate read occur column 6, line 15, after the word and period generator. insert the following claim- 5. The combination with a transmitter, of a pair of modulators, each arranged to impress its characteristic modulation on the transmitter, a pair of switches for controlling said modulators respectively, means for causing taneously, said last mentioned means including a pair of gas discharge tubes, o each having a control electrode; a substantially s uare wave generator, and means for impressing alternately upon said contro electrodes positive pulses derived from the output of said square wave generator.

for the claims now appearing in the patent as 5, 6 and 7 read 6, 7, and 8 respectively; in the heading to the printed specification, line 7, for 7 Claims read 8 Claims; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Ofiice.

Signed and sealed this 2d day of December, A. D. 1947.

THOMAS F. MURPHY,

Assistant Oommz'm'oner of Patents. 

